1. Field of the Invention
The present invention relates to a polarization-independent optical multiplexer/demultiplexer employing an arrayed waveguide grating.
2. Description of the Related Art
The use of silicon (Si) as an optical waveguide material is a technology that has gained attention as a way of mass-producing optical elements and reducing their size. One known type of silicon optical element is an optical multiplexer/demultiplexer. This type of element is used in optical subscriber telecommunication systems to multiplex light of different wavelengths into a single optical fiber and to separate the different wavelengths of light exiting the fiber.
Among the various optical multiplexer/demultiplexer structures, recently there has been much interest in optical multiplexer/demultiplexers employing an arrayed waveguide grating (AWG) structure, which combines good multiplexing and demultiplexing characteristics with small size. One example is described by Kim et al. in ‘Center wavelength uniformity of shallow-etched silicon photonic wire AWG’, Group IV Photonics 2009 IEEE paper ThP6, Sep. 10, 2009.
A silicon AWG optical multiplexer/demultiplexer has the disadvantages of polarization dependency and narrow wavelength passbands. Several Japanese Patent Application Publications (JP) and U.S. Patents (USP) describe structures used to deal with the corresponding problems in quartz waveguides, e.g., JP 2009-20516 (U.S. Pat. No. 7,840,104), JP 2008-058562 (U.S. Pat. No. 7,555,175), JP 2002-14243 (U.S. Pat. Nos. 6,888,985 and 7,194,165), and JP 09-297228 (now Japanese patent No. 3112246). Despite the success of these structures in quartz optical waveguides, however, they have proven difficult to apply to silicon optical waveguides because of the very large wavelength dispersion of silicon optical waveguides.